The hyperuricemia causes gout and renal insufficiency and is also considered to be a factor causing coronary disease. Furthermore, the hyperuricemia is suggested to closely relate to the development of diseases of adults such as hypertension. Therefore, treatment of the hyperuricemia can be effective not only for treating gout but also for preventing various diseases relating to daily nutrition and the advancement of age.
Presently, the hyperuricemia is treated using an inhibitor for inhibiting production of uremic acid such as allopurinol and an accelerator for uricotelism such as benzbromalone. However, it is well known that allopurinol causes side effects such as lesion, hepatopathy, and myelogenetic troubles. The allopurinol and its metabolic product (oxypurinol) are excreted from the kidneys. However, if the excretion of uric acid decreases, the excretion of these compounds also decreases and the concentrations of these compounds in blood increase. Therefore, the chance of causing side effects increases.
It is reported that benzbromalone also causes hepatopathy. Accordingly, it is desired to develop new pharmaceuticals so that the practitioners can select more appropriate pharmaceuticals with less side effects.
Recently, the below-mentioned xanthine oxidase inhibitors having no purine nucleus such as TMX-67 (Teijin Corporation), Y-700 (Mitsubishi Wellpharma Corporation) and KT651 (Kotobuki Corporation) have been reported:

The present inventors have discovered that compounds of the below-mentioned formula (I) containing a bicyclic condensed hetero ring have a xanthine oxidase inhibiting effect. The present invention has been completed based on this discovery.
There are known, as compounds structurally analogous to the compounds of the invention, 2-phenylbenzazole compounds (in Japanese Patent Provisional Publication (Toku-15 hyo) 11-501024) and 2-phenylbenzimidazole compounds (in Japanese Patent Provisional Publication 56-5465). The former compounds have an amino group in the 4th position of the benzene ring and show an antitumor effect, while the latter compounds have 2-hydroxy-3-N-substituted aminopropoxy group in the 4th position of the benzene ring and show a hypotension inducing effect. Accordingly, these compounds differ from the compounds of the invention in their structures and pharmacological effects.